coredns-plugin-action/setup.go

package example

import (
	"github.com/coredns/coredns/core/dnsserver"
	"github.com/coredns/coredns/plugin"
	"github.com/coredns/coredns/plugin/metrics"

	"github.com/mholt/caddy"
)

// init registers this plugin within the Caddy plugin framework. It uses "example" as the
// name, and couples it to the Action "setup".
func init() {
	caddy.RegisterPlugin("example", caddy.Plugin{
		ServerType: "dns",
		Action:     setup,
	})
}

// setup is the function that gets called when the config parser see the token "example". Setup is responsible
// for parsing any extra options the example plugin may have. The first token this function sees is "example".
func setup(c *caddy.Controller) error {
	c.Next() // Ignore "example" and give us the next token.
	if c.NextArg() {
		// If there was another token, return an error, because we don't have any configuration.
		// Any errors returned from this setup function should be wrapped with plugin.Error, so we
		// can present a slightly nicer error message to the user.
		return plugin.Error("example", c.ArgErr())
	}

	// Add a startup function that will -- after all plugins have been loaded -- check if the
	// prometheus plugin has been used - if so we will export metrics. We can only register
	// this metric once, hence the "once.Do".
	c.OnStartup(func() error {
		once.Do(func() {
			m := dnsserver.GetConfig(c).Handler("prometheus")
			if m == nil {
				return
			}
			if x, ok := m.(*metrics.Metrics); ok {
				x.MustRegister(requestCount)
			}
		})
		return nil
	})

	// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
		return Example{Next: next}
	})

	// All OK, return a nil error.
	return nil
}